Autism Spectrum Disorders (ASD) has complex and varying etiologies. A lack of understanding regarding the underlying molecular and cellular mechanisms is a key barrier in finding effective treatments. Single-gene disorders that have a high prevalence of ASD provide unique opportunities to investigate the underlying biology and test treatments for autism. Tuberous Sclerosis Complex (TSC) is a genetic disorder in which approximately 50% of individuals are also affected with ASD. Importantly, TSC can be diagnosed before or at the time of birth, and thus infants with TSC allow us to observe prospectively the natural history of ASD and develop better tools for early detection of autism. On a molecular level, TSC disease manifestations result from the aberrant hyperactivity of mTOR that is caused by mutation in one of two TSC genes. Pharmacologic mTOR inhibition to correct the cellular defects in TSC is no longer a hope for the future, but rather an exciting reality with proven efficacy against various TSC disease manifestations. To determine the potential benefit these agents may have in treating or preventing ASD, it is imperative to identify early markers of autism in infants with TSC, so as to not put young children who will not develop ASD at unnecessary risk. Accumulating clinical and basic science evidence suggests that aberrant white matter connectivity represents a rational candidate as a biomarker in TSC. TSC mouse models demonstrate defects in the specification, guidance, and myelination of axons. More importantly, several groups have reported abnormalities in the normal-appearing white matter of TSC patients that can be identified by MR imaging, and loss of white matter microstructural integrity is associated with neurological and cognitive deficits. Furthermore, there is preliminary data indicating that white matter integrity can be improved by treatment with mTOR inhibitors in both animal models and in TSC patients. Taken together, these findings lead to the hypothesis that longitudinal assessment of white matter integrity and neural connectivity in TSC infants, through advanced MRI and EEG analysis, can be used as an early biomarker of subsequent ASD in this genetic disease. This proposal aims to establish a consortium of five Children's Hospitals that are geographically-distributed throughout the US to recruit TSC patients in the first year of life to test this hypothesis. State of the art imaging with 3Tesla MR scanners, advanced EEG technology, validated neurodevelopmental assessment tools, genetic analysis, and standardized clinical measures through age 36 months will be utilized. The clinical consortium will be supported by a centralized Data Coordinating Center with experience in another rare disease (neurofibro- matosis). Collaboration with Leadership Education in Neurodevelopmental and Related Disabilities (LEND) programs at each center will provide additional interdisciplinary research training and education expertise in ASD and TSC. As a result of the research outlined in this proposal, better understanding of brain connectivity and it relationship to ASD in TSC will pave the way for new interventions for this and related causes of autism.